Random Noise Monopulse Radar System for Covert Tracking of Targets

The University of Nebraska is currently developing a unique monopulse radar concept based on the use of random noise signal for covert tracking applications. This project is funded by the Missile Defense Agency (MDA). The advantage of this system over conventional frequency-modulated continuous wave (FMCW) or short pulse systems is its covertness resulting from the random waveform’s immunity from interception and jamming. The system integrates a novel heterodyne correlation receiver with conventional monopulse architecture. Based on the previous work such as random noise interferometry, a series of theoretical analysis and simulations were conducted to examine the potential performance of this monopulse system. Furthermore, a prototype system is under development to exploit practical design aspects of phase comparison angle measurement. It is revealed that random noise monopulse radar can provide the same function as traditional monopulse radar, i.e., implement range and angular estimation and tracking in real time. The bandwidth of random noise signal can be optimized to achieve the best range resolution as well as the angular accuracy. INTRODUCTION Phase comparison monopulse uses two apertures with displaced phase centers to locate the angle of arrival from scatters. The characteristic of this technique is its dependence on the phase information of received signals. When a random noise transmit waveform is employed, there will be much higher phase uncertainties compared to traditional waveforms due to its random nature. A phase coherent processing technique using the heterodyne correlation architecture has been developed and applied towards polarimetry, Doppler estimation, synthetic aperture (SAR) radar, and inverse SAR (ISAR) with good success. The results obtained compare well with those obtained using conventional waveforms with the added advantage of covertness, i.e., immunity from detection and jamming. One application we have demonstrated that clearly suggests the use of this technique for angular tracking of targets is ultra-wideband (UWB) random noise interferometry. In our experiments, we showed that it was indeed possible to use the phase difference between spaced receiver antennas to locate a target in azimuth, while precise range information was obtained from the target delay. We have also developed the necessary analytical formulation for a clearer understanding of this technique together with its advantages and limitations. Our recent results analyze the applicability of conventional phase-comparison monopulse techniques to the random noise radar system. A monopulse architecture based on sum-and-difference network was used to perform simulation studies. The transmit waveform was assumed to be bandlimited white noise, which was approximated as the summation of a large number of frequency components over the bandwidth, each component having a random amplitude. Received signals are passed through the sum-and-difference hybrid and mixed with a delayed replica of the transmit signal. The intermediate frequency (IF) outputs are routed through band pass filters following which a complex correlation operation is performed. This output provides information on the target direction dynamically. A detailed analysis shows that under ideal conditions, i.e., flat frequency characteristics for the atmospheric propagation as well as for the target reflectance over the operating bandwidth, the output of the monopulse system is identical to that of the single frequency monopulse in the average sense. ANTENNA SYSTEM The antenna is the first component to process the received random noise signal plus uncorrelated system noise. Two special factors influence the performance of random noise monopulse antenna system. The first is signal bandwidth, and the second is the random fluctuations in signal phase and amplitude. For narrowband systems, the antenna pattern is generally well characterized, and is considered invariant over the operating frequency range. However, a UWB waveform operates over a much wider fractional bandwidth, typically greater than 25%. The Report Documentation Page Report Date 29JUL2002 Report Type N/A Dates Covered (from... to) Title and Subtitle Random Noise Monopulse Radar System for Covert Tracking of Targets Contract Number